The present invention relates generally to cellular telecommunication systems, and, more particularly, to a method and system for controlling radio channel congestion in a cellular telecommunications system.
The cellular telephone industry has made phenomenal strides in commercial operations in the United States as well as the rest of the world. Growth in major metropolitan areas has far exceeded expectations and is rapidly outstripping system capacity. If this trend continues, the effects of this industry""s growth will soon reach even the smallest markets. Innovative solutions are required to meet these increasing capacity needs as well as maintain high quality service and avoid rising prices.
FIG. 1 is a block diagram that illustrates a cellular telecommunications system 100. The cellular system 100 includes a plurality of radio base stations 140a-n, 140a-nxe2x80x2, each being connected to a corresponding antenna 130a-n, 130a-nxe2x80x2. The radio base stations 140a-n, 140a-nxe2x80x2, in conjunction with the antennas 130a-n, 130a-n40 , communicate with a plurality of mobile stations (e.g., mobile stations 120a, 120b, 120m, 120axe2x80x2, 120bxe2x80x2 and 120mxe2x80x2), which are located in one of the cells 110a-n, 110a-nxe2x80x2. Communication from a base station to mobile stations are transmitted on downlink (DL) radio channels of the base station.
In general, a mobile station communicates with the base station corresponding to the cell in which the mobile station is located or if the system supports soft handovers, a mobile station would communicate with more than one base stations. In FIG. 1, for example, mobile stations 120a and 120b are shown to be communicating with base station 130a. The base stations 130a-n are, in turn, connected to the radio network controller (RNC) 150, whereas the base stations 130a-nxe2x80x2 are connected to the RNC 150xe2x80x2. Mobile control node 160 is a switching center that supports the interconnection of the cellular system 100 to a fixed network 170 by landlines or other equivalent connections. The fixed network 170 may comprise a computer-based network (e.g., the Internet), a public switched telephone network (PSTN), an integrated services digital network (ISDN) or a public data network (PSPDN).
As more mobile stations subscribe to these types of systems, the demand for system capacity will increase rapidly, especially in highly populated areas, and one of the most crucial limiting factors for the system DL capacity of the radio channel is the available DL transmit power, PDLxe2x80x94MAX, of the base stations. Thus, for example, if the number of mobile stations being serviced by a given base station is excessive, the base station may not have sufficient DL transmit power available to provide effective support. Consequently, mobile stations may experience transmission delays and unserved requests due to the congestion of the radio channel.
Therefore, a need exists for a method and system for monitoring potential radio channel congestion and for relieving congestion on one or more radio channels of a cellular system.
The present invention involves method and system for monitoring potential congestion on radio channels, and when appropriate, relieving the radio channel congestion. In general, the present invention accomplishes this through the use of a radio channel congestion alarm that continuously monitors DL transmit power of a base station and compares the current DL transmit power level to an alarm threshold value. The alarm threshold value, in turn, is adaptively adjusted as a function of the variation over time in DL transmit power of the base station. By adaptively adjusting the alarm threshold value based on the variation over time of the DL transmit power, the method and/or system of the present invention monitors potential radio channel congestion based on the behavior of DL transmit power, which increases the accuracy of the congestion alarm, improves the congestion relief and enhances the system capacity.
When appropriate, the present invention relieves radio channel congestion using a congestion controller. The congestion controller is divided into a fast congestion controller (FCC) located in the base station and a slow congestion controller (SCC) located in a radio network controller. The FCC performs rapid congestion relief actions to mitigate DL radio channel congestion until the SCC permanently resolves DL radio channel congestion.
Accordingly, it is an object of the present invention to more accurately detect potential DL radio channel congestions.
It is another object of the present invention to eliminate false congestion alarms and unnecessary capacity limiting actions.
It is yet another object of the present invention to provide fast congestion relief actions upon detecting potential DL radio channel congestion.
It is another object of the present invention to efficiently relieve DL radio channel congestion without decreasing the system DL capacity.
In accordance with one embodiment of the present invention, the above-identified and other objectives are achieved by a base station comprising a FCC. The FCC monitors potential radio channel congestions by monitoring characteristics of the DL transmission on radio channels of the base station. The FCC comprises a congestion alarm having an alarm threshold value that is adaptively adjusted based on the characteristics of DL transmission. Specifically, the variation over time of the DL transmit power is determined and used to adjust the FCC alarm threshold value. Further, the FCC alarm threshold value can be adaptively adjusted with respect to the variation over time of the DL transmit power, the detected number of users and their offered bit rates.
Further, according to exemplary embodiments of the present invention, upon detecting radio channel congestions, methods and systems for relieving radio channel congestions include temporarily blocking data services in the system. Specifically, when the base station is not servicing any packet data user, the system then temporarily reduces the maximum transmit power allowed for all users"" downlink dedicated physical channels (DPCHs). However, when there are packet data users serviced by the base station, the system then temporarily blocks packet data services by rapidly decreasing transmit power of the packet data users"" downlink DPCHs.